Our program is focused on studying the biochemistry and physiology of the nerve terminal using the neurohypophysial neuroendocrine cells as the model system. A preparation of highly purified neurosecretosomes (nerve endings from the neurosecretory neurons) was developed. This preparation forms the unique experimental system to study various aspects of nerve terminal function. Membrane systems obtained by disruption of the neurosecretosomes were fractionated and ATP-dependent Ca2+ accumulating membranes were identified. Furthermore, permeabilizing the plasma membrane by the use of digitonin or saponin has provided access to study intra-terminal Ca2+ accumulating systems. The neurosecretosomes have been successfully immobilized onto solid matrices so that the kinetics of Ca2+-dependent secretion can be monitored. The presence of opiate receptors on the nerve ending membranes was identified and characterized. The kappa type opiate receptor is predominantly present on neurosecretory nerve endings. Studies on isolated neurosecretory vesicles have led to the identification of both a Ca2+- activated cation channel of large conductance level (greater than 400Ps) and an anion channel. These channels may be important in the mechanism of exocytotic secretion at the nerve terminal.